The present invention generally relates to a picture processing apparatus for processing a picture photographed by a photographing device. More specifically, the present invention relates to a picture processing apparatus with a photographing device and a storing portion disposed on the same circuit thereby accelerating a calculating process, and to a picture processing apparatus for suppressing characteristics of the storing portion from fluctuating even if a temporal change in brightness of an object is diminutive, thereby ensuring an accurate calculation output.
With a picture of an object photographed as a first frame and a picture of the object photographed as a second frame, the temporal change in brightness of the object can be obtained.
Conventionally, when the difference between pictures is obtained, a camera that is equipped with a photographing device such as a CCD (Charge Coupled Device), a plurality of frame memories, and a calculating apparatus are prepared and connected. In other words, picture data of a first frame that is output from the camera is temporarily stored in a frame memory. Thereafter, picture data of a second frame that is photographed is stored in another frame memory. The calculating apparatus synchronously reads the contents (namely, picture data) stored in the frame memories and calculates the difference of the corresponding pictures.
However, since picture data is transferred from the camera to the frame memories in the serial method, the transfer time for one screen can be rather long. For example, in an NTSC (National Television System Committee) type camera of which the CCD is used as a photographing device, while a picture of one frame is being photographed, a picture of the preceding frame is read. Thus, until a picture of one frame is read and transferred, it takes as long as 33 msec. Consequently, after a picture is photographed, until the calculated result is obtained, it takes at least 33 msec.
FIG. 10 shows a timing chart of which a photographed picture is stored and read in the CCD as a photographing device. As shown in FIG. 10, it takes 33 msec until a picture of each of odd fields and even fields is stored. Additionally, as shown in FIG. 10, unless the read period for a picture of the second frame elapses, the calculated result cannot be obtained.
Thus, it is difficult to apply the conventional photographing system using a camera composed of a CCD photographing device to a controlling system using visual information such as visual feedback.
Conversely, in a prototype CMOS image sensor, the frame rate is raised to as high as around 1 kHz and while pictures are being photographed at very high speed, a calculating process is successively performed so as to accomplish the visual feedback. However, in such a sensor, since internal processes are digitally performed, it is necessary to provide, for example, an A/D converting circuit for converting analog values into digital values, a storing circuit for storing digital values, and a calculating circuit for calculating digital values. Since these circuit modules have large circuit scales, they are not suitable for a many-pixel device. Thus, it is difficult to commercially use such a sensor (refer to “Designing ultra parallel, ultra high speed vision chip using general purpose processing element (translated title)” by Komuro et. al., Journal of The Institute of Electronics, Information and Communication Engineers, Japan, Vol. J81-D-1, No. 2, pp. 70–76, 1998).
Additionally, a CMOS image sensor for calculating analog signals as they are has been proposed. In such sensors, a memory function is accomplished by storing a signal voltage to a capacitor. Thus, depending on how a capacitor is structured, each pixel becomes large. Even if the number of pixels can be increased by disposing a memory portion at a non-pixel area, such a method is not suitable for reducing the size of the chip.
Also, when a signal voltage is stored to a capacitor, if a signal voltage of another capacitor is read as a gate voltage of another transistor, since threshold voltages of individual transistors fluctuate, there is a risk that a signal may be read as a different value. As a result, the calculated result may contain an error. In addition, when a signal voltage is stored to a capacitor, since the charging time cannot be ignored, such sensors are not suitable for high speed processes.